The present invention relates to a method of fabrication of a semiconductor integrated circuit device and to a mask making technique; and, more particularly, the invention relates to a technique that is effective when applied to an exposure process using a phase shift mask.
An edge-enhanced phase shift mask is one type of phase shift mask. It has, on the main surface of a mask substrate that is transparent relative to an exposure light, a light shielding film made of metal, such as chromium, a light transmitting region formed by an opening in a portion of the light shielding film, and a transparent phase shifter, at the periphery of the light transmitting region (at the edge portion in the vicinity of the boundary with the light shielding film), for inverting the phase of light transmitted through the light transmitting region by 180°. In the edge-enhanced phase shift mask, by optimizing the edge width according to the transmittance of the edge portion, it is possible to attain an almost similar level of resolving performance improving effect at any transmittance.
With regards to the edge-enhanced phase shift mask, Japanese Unexamined Patent Publication No. Hei 11(1999)-65083, for example, discloses a technique for transferring hole patterns onto a semiconductor wafer by using a photomask which has mask hole patterns having a maximum transmittance, medium transmittance patterns at the periphery thereof, causing light which has transmitted through the mask hole patterns to have a phase difference of 180°±60°, and patterns formed at the periphery of the medium transmittance patterns and having a minimum transmittance.
Japanese Unexamined Patent Publication No. Hei 11(1999)125894, discloses a technique for transferring patterns of a desired size onto a semiconductor wafer by using a photomask having some transparent regions whose mask patterns are made larger than a predetermined size, a semitransparent region disposed at the periphery of each of the transparent regions, having a predetermined width and forming a reverse phase relative to light transmitted through the transparent region, and a light shielding region disposed at the periphery of the semitransparent region.
Japanese Unexamined Patent Publication No. Hei 10(1998)326009, discloses a pattern transferring technique through use of a phase shift mask which has phase shift patterns, at the periphery of each of a plurality of main light transmitting regions, having a lower transmittance than that of the main light transmitting regions, wherein the width of some phase shift patterns which particularly require edge enhancement, among these phase shift patterns, is made greater than that of the other ones.